The present invention relates generally to medical devices and methods and, more particularly, to a programmable, microprocessor based controller and method for controlling the temperature and flow of a thermal exchange fluid that is circulated through a heat exchange catheter inserted into a patient""s body for the purpose or cooling or warming at least a portion of the patient""s body.
Under ordinary circumstances, the thermoregulatory mechanisms of a healthy human body serve to maintain the body at a constant temperature of about 37xc2x0 C. (98.6xc2x0 F.), a condition sometimes referred to as normothermia. To maintain normothermia, the thermoregulatory mechanisms act so that heat lost from the person""s body is replaced by the same amount of heat generated by metabolic activity within the body. For various reasons such as extreme environmental exposure to a cold environment or loss of thermoregulatory ability as a result of disease or anesthesia, a person may develop a body temperature that is below normal, a condition known as hypothermia. A person may develop a condition that is above normothermia, a condition known as hyperthermia, as a result of extreme exposure to a hot environment, or malfunctioning thermoregulatory mechanisms, the latter being a condition sometimes called malignant hyperthermia. The body may also establish a set point temperature (that is, the temperature which the body""s thermoregulatory mechanisms function to maintain) that is above normothermia, a condition usually referred to as fever.
Accidental hypothermia is generally a dangerous condition that may even be life threatening, and requires treatment. If severe, for example where the body temperature drops below 30xc2x0 C., hypothermia may have serious consequences such as cardiac arrhythmias, inability of the blood to clot normally, or interference with normal metabolism. If the period of hypothermia is extensive, the patient may even experience impaired immune response and increased incidence of infection.
Simple methods for treating accidental hypothermia have been known since very early times. Such methods include wrapping the patient in blankets, administering warm fluids by mouth, and immersing the patient in a warm water bath. If the hypothermia is not too severe, these methods may be effective. However, wrapping a patient in a blanket depends on the ability of the patient""s own body to generate heat to re-warm the body. Administering warm fluids by mouth relies on the patient""s ability to swallow, and is limited in the temperature of the liquid consumed and the amount of fluid that may be administered in a limited period of time. Immersing a patient in warm water is often impractical, particularly if the patient is simultaneously undergoing surgery or some other medical procedure.
More recently, hypothermia may be treated in a more complex fashion. Heated warming blankets may be applied to a patient or warming lamps that apply heat to the skin of the patient may be used. Heat applied to the patient""s skin, however, has to transmit through the skin by conduction or radiation which may be slow and inefficient, and the blood flow to the skin may be shut down by the body""s thermoregulatory response, and thus, even if the skin is warmed, such mechanisms may be ineffective in providing heat to the core of the patient""s body. When breathing gases are administered to a patient, for example a patient under anesthesia, the breathing gases may be warmed. This provides heat relatively fast to the patient, but the amount of heat that can be administered without injuring the patient""s lungs is very limited. An alternative method of warming a hypothermic patient involves infusing a hot liquid into the patient via an IV infusion, but this is limited by the amount of liquid that can be infused and the temperature of the liquid.
In extreme situations, a very invasive method may be employed to control hypothermia. Shunts may be placed into the patient to direct blood from the patient through an external machine such as a cardiopulmonary by-pass (CPB) machine which includes a heater. In this way, the blood may be removed from the patient, heated externally, and pumped back into the patient. Such extreme measures have obvious advantages as to effectiveness, but also obvious drawbacks as to invasiveness. The pumping of blood through an external circuit that treats the blood is generally quite damaging to the blood, and the procedure is only possible in a hospital setting with highly trained personnel operating the equipment.
Accidental hyperthermia may also result from various conditions. Where the normal thermoregulatory ability of the body is lost, because of disease or anesthesia, run-away hyperthermia, also known as malignant hyperthermia, may result. The body may also set a higher than normal set point resulting in fever which is a type of hyperthermia. Like hypothermia, accidental hyperthermia is a serious condition that may sometimes be fatal. In particular, hyperthermia has been found to be neurodestructive, both in itself or in conjunction with other health problems such as traumatic brain injury or stroke, where a body temperature in excess of normal has been shown to result in dramatically worse outcomes, even death.
As with hypothermia, when the condition is not too severe, simple methods for treating the condition exist, such as cold water baths and cooling blankets, or antipyretic drugs such as aspirin or acetaminophen, and for the more extreme cases, more effective but complex and invasive means such as cooled breathing gases, cold infusions, and blood cooled during CPB also exist. These, however, are subject to the limitations and complications as described above in connection with hypothermia.
Although both hypothermia and hyperthermia may be harmful and require treatment in some cases, in other cases hyperthermia, and especially hypothermia, may be therapeutic or otherwise advantageous, and therefore may be intentionally induced. For example, periods of cardiac arrest or cardiac insufficiency in heart surgery result in insufficient blood to the brain and spinal cord, and thus can produce brain damage or other nerve damage. Hypothermia is recognized in the medical community as an accepted neuroprotectant and therefore a patient is often kept in a state of induced hypothermia. Hypothermia also has similar advantageous protective ability for treating or minimizing the adverse effects of certain neurological diseases or disorders such as head trauma, spinal trauma and hemorrhagic or ischemic stroke. Therefore it is sometimes desirable to induce whole-body or regional hypothermia for the purpose of facilitating or minimizing adverse effects of certain surgical or interventional procedures such as open heart surgery, aneurysm repair surgeries, endovascular aneurysm repair procedures, spinal surgeries, or other surgeries where blood flow to the brain, spinal cord or vital organs may be interrupted or compromised. Hypothermia has even been found to be advantageous to protect cardiac muscle tissue after a myocardial infarct (MI).
Current methods of attempting to induce hypothermia generally involve constant surface cooling, by cooling blanket or by alcohol or ice water rubs. However, such cooling methods are extremely cumbersome, and generally ineffective to cool the body""s core. The body""s response to cold alcohol or ice water applied to the surface is to shut down the circulation of blood through the capillary beds, and to the surface of the body generally, and thus to prevent the cold surface from cooling the core. If the surface cooling works at all, it does so very slowly. There is also an inability to precisely control the temperature of the patient by this method.
If the patient is in a surgical setting, the patient may be anesthetized and cooled by CPB as described above. Generally, however, this is only available in the most extreme situations involving a full surgical team and full surgical suite, and importantly, is only available for a short period of time because of the damage to the blood caused by pumping. Generally surgeons do not wish to pump the blood for periods longer than 4 hours, and in the case of stroke or traumatic brain damage, it may be desirable to induce hypothermia for longer than a full day. Because of the direct control of the temperature of a large amount of blood, this method allows fairly precise control of the patient""s temperature. However, it is this very external manipulation of large amounts of the patient""s blood that makes long term use of this procedure very undesirable.
Means for effectively adding heat to the core of the body that do not involve pumping the blood with an external, mechanical pump have been suggested. For example, a method of treating hypothermia or hyperthermia by means of a heat exchange catheter placed in the bloodstream of a patient was described in U.S. Pat. No. 5,486,208 to Ginsburg, the complete disclosure of which is incorporated herein by reference. Means of controlling the temperature of a patient by controlling such a system is disclosed in U.S. Pat. No. 5,837,003, also to Ginsburg, the complete disclosure of which is incorporated herein by reference. A further system for such controlled intervascular temperature control is disclosed in publication WO 00/10494 to Ginsburg et al., the complete disclosure of which is incorporated herein by reference. Those patents and publication disclose a method of treating or inducing hypothermia by inserting a heat exchange catheter having a heat exchange area into the bloodstream of a patient, and circulating heat exchange fluid through the balloon while the balloon is in contact with the blood to add or remove heat from the bloodstream. (As used herein, a balloon is a structure that may be readily inflated by increasing pressure in the balloon and collapsed by reducing pressure in the balloon vacuum.)
For the foregoing reasons, there is a need for a rapid and effective means to add or remove heat from the fluid supply for a catheter used to control the body temperature of a patient in an effective and efficient manner, while avoiding the inadequacies of the prior art methods. In particular, a fluid source that rapidly, efficiently and controllably regulates a disposable source of fluid based on feedback from the temperature of the patient or target tissue within the patient would be a great advantage.
The invention provides for modification and control of the temperature of a patient, or selected portions of a patient, including controllably inducing a state of hypothermia in the patient. The invention also provides for controllably warming a patient in whom a state of reduced temperature, or hypothermia, has been induced.
In one embodiment, the present invention includes a heat transfer catheter insertable into a patient, a disposable heat exchange plate, conduits coupled to the heat transfer catheter and heat exchange plate that enable circulation of a heat exchange medium therebetween, and a master control unit housing a heater/cooler unit within and having a slot, the slot being sized so that the disposable heat exchange plate can be installed therethrough into the master control unit and into thermal communication with the heater/cooler unit, wherein the heater/cooler unit can influence the temperature of the patient via the disposable heat exchange plate, conduits, and heat transfer catheter.
In another embodiment, the invention includes a heat transfer catheter insertable into a patient, a disposable heat exchange unit having a fluid pathway therewithin and incorporating an integral pump head adapted to move fluid through the fluid pathway, conduits coupled to the heat transfer catheter and heat exchange unit that enable circulation of a heat exchange medium therebetween upon operation of the pump head, and a reusable master control unit having a heater/cooler and a pump driver, the disposable heat exchange unit being adapted to couple to the master control unit such that the pump driver engages the integral pump head and so that the fluid pathway is in thermal communication with the heater/cooler.
In another embodiment, the present invention may also include a plurality of sensors that supply patient data, such as the patient""s temperature, to a master control unit that is adapted, configured or programmed to operate a heater/cooler based on the supplied patient data. The master controller may include a microprocessor that is responsive to the sensors to provide control signals to the heater/cooler. The microprocessor may also be configured or programmed to compare signals from at least two of the sensors and produce an alarm signal if the signals do not agree.
In still another embodiment, the microprocessor may receive a target temperature input and a sensor signal that represents a sensed patient temperature. The microprocessor is configured or programmed to add heat to the heat exchange medium if the target temperature is above the patient temperature and remove heat from the heat exchange medium if the target temperature is below the patient temperature in response to the signal from the sensor with a proportional integrated differential (PID) response such that the rate at which patient temperature approaches the target temperature is controlled.
In another embodiment the present invention provides a method for regulating the temperature of at least a portion of a patient. The method includes providing a disposable heat transfer catheter and heat exchange unit coupled via conduits that enable circulation of a heat exchange medium therebetween, providing a master control unit housing a heater/cool unit within and having a slot, installing the heat exchange unit through the slot into the master control unit and into thermal communication with the heater/cooler unit, inserting the heat transfer catheter into the patient, circulating fluid between the heat transfer catheter and heat exchange unit in the master control unit, and transferring heat between the heat exchange unit and a heater/cooler unit so as to regulate the temperature of the patient via the heat transfer catheter.
In still another embodiment, the method of regulating the temperature of at least a portion of a patient may include sensing the patient""s body temperature, providing a heat transfer region on the heat transfer catheter, the heat exchange plate, heater/cooler, and pump head being adapted to flow heat exchange medium through the conduits to elevate or depress the temperature of the catheter heat transfer region relative to the body temperature, selecting a target temperature different than the body temperature, selecting a ramp rate equal to the time rate of change of temperature from the body temperature to the target temperature, setting the temperature of the heat exchange medium within the catheter heat transfer region based on the ramp rate, monitoring the temperature differential between the target temperature and the body temperature, and reducing the ramp rate when the temperature differential reduces below a predetermined threshold.
In yet another embodiment, the present invention provides a method of circulating a heat exchange medium through a heat transfer catheter installed in the body of a patient, the method including providing a disposable heat transfer catheter and heat exchange unit coupled via conduits that enable circulation of a heat exchange medium therebetween, the heat exchange unit incorporating an integral pump head adapted to circulate fluid through the conduits, providing a reusable master control unit having a pump driver, coupling the heat exchange unit to the master control unit such that the pump driver engages the integral pump head, inserting the heat transfer catheter into the patient, and actuating the pump driver to circulate fluid between the heat transfer catheter and heat exchange unit.
Other features and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.